Safeway Inc. bagged hefty gains following a Reuters report late Tuesday that a handful of buyout firms, including Cerberus Capital Management, are exploring a deal for all or part of the chain. California-based Safeway is the second-largest mainstream US grocery store operator, with a market value of over $8 billion. Jana Partners LLC reported a 6.2 percent stake in Safeway in September, called the shares undervalued, and held talks with management. Safeway adopted a “poison pill” plan to prevent an unwanted takeover.